Physical electromechanical structures particularly large rotating machines such as turbine generators and propulsion drive units generate unwanted noise or vibrations involving both rotational and translatory motion. Various methods and structures have been used in the past to reduce, isolate or eliminate such undesirable vibration signals.
It has been known, for example, to isolate vibrations by way of passive restraint systems such as resilient mounts, springs, the addition of large masses or dampening devices such as shock absorbers and the like. Such passive systems have varied from simple to complex but have normally added substantially to the weight and mass of a system.
Active noise suppression or cancellation systems have also been known and used in the prior art. Such systems are known to be relatively small and light with respect to passive noise suppression or cancellation systems but are normally far more complex than the passive systems. Such active systems, for example, normally operate by introducing a noise into the vibrating or noisy structure as an additional noise to that which exists in the system. Such introduced noise is carefully controlled so that the original and induced noises will combine in such a manner as to obtain cancellation through destructive interference. The process is performed by measuring noise or vibration signals from one or more sensing devices and in accordance with an analysis of the sensed noise adding the exactly opposite noise through a like number of actuation devices to obtain a net reduction or substantial cancellation of system noise. Such noise cancellation or nulling systems typically involve a plurality of separate channels wherein each channel includes a sensor and an actuator.
I have discovered, however, that a difficulty arises in such systems since there is often an interaction between the separate channels. That is to say, commercially available control systems for noise cancellation principally operate as single channel controllers wherein for each such channel there is a single input and a single output signal. Under many conditions the individual channels interact and result in an unstable condition in which excessively large and potentially damaging signals are produced by the system to be controlled. For example, where strong interaction between channels occurs, the noise required to silence one channel may interact with another channel and increase the noise of the latter channel. Such a condition can cause the control system to erroneously increase the induced or compensating noise in certain channels while minimizing the noise in others. Moreover, such unstable systems may operate repetitively in such a manner and thus result in higher and higher noise as well as system damage.
It is, therefore, the principle object of the present electronic compensation system to provide a means for electronically separating the channels and allowing the noise cancellation system to operate as intended.
It is a further object of the disclosed system to provide a means and method of electronically combining the signals from two or more interacting channels in such a manner as to create new channels which do not interact but which allow the existing control systems to operate effectively in applications and environments in which they were previously ineffective.
It is a still further object of the exemplary embodiments disclosed herein to provide a means and manner for combining the signals of the parallel channels of commercially available noise cancellation control systems that are not stable under certain conditions so that such channels are decoupled as to the modes of vibration of a structure in such manner as to maintain stability.
It is a still further object of the disclosed inventive subject matter to provide an electronic compensation system and method wherein signals from multiple input sensors are preprocessed for connection to the control system as well as being additionally processed prior to their connection with the noise injecting actuators. The compensation network includes active devices for combining two or more signals into a single signal wherein the single signal would be then processed by the control system to generate an anti-noise control channels is then passed through post-processing compensation steps before being fed to two or more anti-noise signal injecting actuators.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.